The present invention relates to systems and methods for controlling harmful exhaust gas emissions produced by an internal combustion engine using an exhaust gas recirculation circuit.
The use of alternative charge air handling and turbocharging concepts to drive and control exhaust gas recirculation (EGR) as a primary means for reducing harmful exhaust emissions in automotive and truck engines is in widespread use today. One of the more popular approaches is to use a single stage variable geometry turbocharger (VGT) in combination with an EGR circuit to achieve the desired ratio of EGR rate and fresh air/fuel ratio. Typically, the EGR circuit at a minimum, includes a EGR valve, a cooler, tubing connecting the exhaust side of the engine with the intake side of the engine. The EGR valve may be an on/off or a modulating type to regulate EGR flow and it may be mounted on the turbine, exhaust manifold, or on the downstream cool side of the EGR cooler. Alternatively, the EGR circuit may include a mixing device at the point of the EGR gas entry into the intake and/or venturi device to encourage a negative pressure differential across the engine as required to drive EGR flow from the exhaust side to the intake side of the engine.
In many diesel engines, particularly large engines under low speed and moderate to high load operation, the turbocharger match is relatively efficient. Therefore, intake side pressure levels will usually exceed exhaust side pressure and a positive pressure differential exists across the engine under a wide range of steady state or near steady state operating conditions. However, to drive EGR from the exhaust to the intake side of the engine, a negative pressure differential must be created for all or part of the engine cycle. In some exhaust gas treatment systems, the VGT forms the primary role of reversing the pressure differential across the engine. However, during the breathing portion of the four stroke cycle, engine pumping parasitics and brake specific fuel consumption (BSFC) are increased. As the turbine vanes are moved toward a closed position, turbocharger compressor wheel speeds increase as does overall boost levels. Depending on the contour of the turbine and compressor efficiency maps versus gas flow and boost, turbine and compressor efficiencies will eventually begin to deteriorate as the wheel speeds and boost increase. Turbine-in pressure (engine exhaust pressure) will ultimately exceed compressor out pressure (engine intake pressure) thereby creating the necessary overall negative pressure differential across the engine. Manifold gas dynamics and associated pressure pulses will enable some amount of EGR to begin to flow even though the cycle average pressure differential across the engine is slightly positive. If moderate to large EGR flow rate percentages are required, the cycle average pressure differential will become negative.
One challenge for a production feasible diesel engine EGR system is the repeatable control of EGR and fresh air/fuel ratios under all modes of normal and regulated operation and over the life of the engine. Depending on the turborcharger-engine match and gas dynamic characteristics of a given engine/EGR system, EGR flow rates can be highly sensitive to geometry of the VGT/EGR circuit. It is not unusual for EGR flow rates and BSFC to be increasingly sensitive to the geometry and position of the VGT vanes, as local turbine gas velocities increase, especially under high load/low speed operation. Tolerance stackups of VGT and EGR circuit hardware can yield an imposing challenge to achieve equal EGR rates from engine to engine, even when the engine is new. As parts begin to wear and accumulate normal levels of residue, the flow characteristics of the EGR circuit are affected. The ability to manage the appropriate ratio of EGR flow and fresh engine air flow via control logic for controlling the VGT circuit and the EGR valve becomes increasingly difficult.
Therefore, a need exists for a new and improved system for managing the appropriate ratio of EGR circuit flow and fresh engine air flow. The new and improved system must compensate for tolerance stackups of the VGT and EGR circuit hardware.
In accordance with an aspect of the present invention, an exhaust gas treatment system for use in an internal combustion engine for treating exhaust gases, wherein the internal combustion engine has an engine exhaust gas manifold and an engine air intake manifold is provided. The exhaust gas treatment system has an exhaust gas recirculation valve in communication with the engine exhaust gas manifold and engine air intake manifold. The valve directs engine exhaust gas toward the engine air intake manifold. Further, a pump is disposed between the engine air intake manifold and the exhaust gas recirculation valve to create a pressure differential to facilitate the exhaust gas to flow from the engine exhaust gas manifold to the engine air intake manifold.
In accordance with another aspect of the present invention, a cooler is disposed between the pump and the exhaust gas recirculation valve for cooling the engine exhaust gases before the exhaust gases reach the engine air intake manifold.
In accordance with still another aspect of the present invention, a gas turbine circuit is provided for supplying charged air to the engine air intake manifold.
In accordance with still another aspect of the present invention, the gas turbine circuit further comprises a gas turbine and a compressor.
In accordance with still another aspect of the present invention, the gas turbine is a variable geometry turbine.
In accordance with still another aspect of the present invention, the pump is a small meter pump.
In accordance with yet another aspect of the present invention, the EGR valve is an on/off valve.
In accordance with yet another aspect of the present invention, the EGR valve is a modulating valve.
In accordance with yet another aspect of the present invention, the pump is disposed between the cooler and the engine air intake manifold.
In accordance with yet another aspect of the present invention, the pump is capable of providing real-time measurement of exhaust gas recirculation flow rates.
In accordance with yet another aspect of the present invention the pump has a pressure range of between 0 to 0.2 bar.
In accordance with yet another aspect of the present invention a method is provided for treating engine exhaust gases produced by an internal combustion engine. The internal combustion engine has an exhaust gas recirculation circuit which diverts engine exhaust gas from an engine exhaust gas manifold to an engine air intake manifold. The method includes diverting the engine exhaust gases toward the engine air intake manifold using an exhaust gas recirculation valve and creating a pressure differential for enabling the engine exhaust gas to flow from the engine exhaust gas manifold to the engine air intake manifold using a pump disposed between the engine air intake manifold and the exhaust gas recirculation valve.
The above features, benefits and advantages and other features, benefits and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken together with the accompanying drawings.